Analogue-to-digital converters providing multi-stage noise-shaping, known as MASH, by employing cascaded delta-sigma (ΔΣ) modulators are efficient and scalable when implemented using discrete-time switched-capacitor circuits. Such analogue-to-digital converters are very useful for cellular receivers which are required to support both a narrowband standard, such as Global System for Mobile Communication (GSM), and a wideband standard, such as the Third Generation Partnership Project Long Term Evolution (3GPP LTE), also known as LTE, with small circuit footprint and high energy efficiency.
By using continuous-time circuits, rather than discrete-time switched-capacitor circuits, analogue baseband filtering can be relaxed in cellular receivers and, in measurement receivers, no separate analogue baseband filter block may be required. However, a separate noise cancellation filter is required in the digital domain with the MASH scheme, and the use of such a noise cancellation filter requires matching of analogue and digital domain transfer functions. This matching is difficult to maintain in continuous-time circuits without calibration against process variation and temperature drift.
Therefore, there is a requirement for an improved analogue-to-digital converter and method of analogue-to-digital conversion.